Free fall is a uniformly accelerated motion of any object only under the influence of gravity.
The movement of the moon around the earth is an example of the free fall of the Moon under the gravitation region of the earth. Even all planets around the sun are free to fall a fixed orbit under the gravitation region of the sun.
Nearly 400 years ago, Galileo Galilei introduced the concept of free fall, while finding the relation between time and distance covered by different objects at different angles.
Step2: Free-fall hypothesis
Galileo conducted an experiment by rolling a ball on an inclined plane.
He observed that the ratio of the distance covered to the square of the corresponding time was always the same. The experiment was also true for different angles of inclination.
Finally, he stated that when the angle of the inclined surface was 90o with the ground the ball falls down to the earth which is a free fall of the ball. He also deduced that the ratio of distance and square of the time taken for the fall is always constant for the free fall.